In thermal nuclear fusion by inertial confinement, laser or electron beams are applied uniformly about a hollow sphere containing a gas such as a mixture of deuterium and tritium. Research on such methods has typically been conducted using glass shells of about 100 .mu.m (micrometer) outer diameter and 1 .mu.m wall thickness, although target sizes ranging from one to ten millimeters have been considered. The high intensity beams applied to the shell causes heating and vaporization of the shell, and the shell vapors cause radial compression of the fusible gas therewithin. It may be noted that ablation shells have also been suggested which ablate an exterior layer and the rest of the shell implodes by reaction forces. In any of these situations, it is important that the shells have thin walls so that they are heated to as high a temperature as possible for beams of given energy, and that the inner and outer spherical walls be precisely concentric to obtain a uniform implosion of the fusible gas within the shell. It has been found that shell forming techniques such as the dropping of gas-filled bodies through a vertical tube furnace, produces only a small percentage of precisely concentric spherical bodies. The percentage of hollow spheres with precisely concentric inner and outer surfaces decreases as the aspect ratio (ratio of outer sphere diameter to wall thickness) increases and as the diameter of the sphere increases. Glass shells with aspect ratios as high as 500:1 have been produced, but only one sphere out of many thousands that are produced will be sufficiently concentric to be usable. A concentricity which results in a maximum wall thickness no more than about 1% greater than the minimum wall thickness may be considered a minimum precision of concentricity to be acceptable in inertial confinement fusion applications. A system which produced high aspect ratio gas-filled spheres, wherein a high proportion of the spheres have precisely concentric inner and outer surfaces, would be of considerable value in the production of targets for thermonuclear fusion by inertial confinement, and in any other applications where concentric spheres were needed.